Siemens 3RT20351AC20 Electromechanical Contactor

Overview

The 3RT20351AC20 is a Siemens Sirius industrial contactor in the 3RT2035 series (Size S2). The "C" in the ordering code designates a 24 VAC rated coil; the "20" suffix indicates one normally-open auxiliary contact (1NO). The data source lists a contact current rating of 60 A for the seed, while the nominal full-load current rating for the series is stated as 40 A—these two figures require explicit confirmation in the Siemens 3RT2 datasheet to establish the thermal endurance margin and coordination class. The coil operates between approximately 20.4 VAC and 28.8 VAC (85–110% of 24 VAC nominal).

Key Parameters

Verification required before selection:

• Switching voltage (max) — not listed; critical for motor branch and coordination studies.
• Breaking capacity / AC-3 utilization category ratings — not listed; needed for short-circuit coordination and overload relay matching.
• Dielectric strength / impulse voltage — not listed.
• Electrical endurance (cycles at rated current) — not listed.
• Coil release (drop-out) voltage — not listed in seed specs.

Do not proceed with coordination calculations or short-circuit coordination studies without these values from the official Siemens 3RT2 datasheet.

Coil and Control Characteristics

The coil is rated at 24 VAC with a must-operate threshold of 20.4 VAC (~85% of nominal). Coil inrush power is listed as 210 VA, which reflects the high locked-rotor inrush of an AC electromagnet; confirm the holding (sealed) power figure from the datasheet to correctly size the control transformer or power supply.

Operate time is 80 ms; the release time field is absent from the seed record. Release time is relevant for cascade coordination in motor starting sequences where intentional sequencing of contactor dropout matters.

Operating temperature range is 25°C to 60°C. For panels in non-conditioned environments, verify whether the full-load current must be derated above 40°C, which is common for Size S2 devices.

Contact Arrangement

The seed carries a 3PST-NO (3 Form A) main pole arrangement and includes one normally-open auxiliary contact (1NO) as indicated by the "20" suffix in the ordering code. Auxiliary contact type and current rating (typically 6 A or 10 A for the Siemens 3RT series) is not broken out in the catalog fields; confirm from the datasheet before specifying for control-circuit use.

The seed is encapsulated in Bulk packaging. Several alternates in the 3RT20351Axxx family list Box packaging instead; confirm the unit pack quantity and any minimum order requirements if bulk feeding of automated assembly lines is intended.

Integration Notes

• Mounting: Both chassis mount and DIN rail (35 mm) are listed; the DIN rail adapter is standard on the 3RT2 series.
• Terminal style: Screw-type terminals per the catalog title; confirm wire range and torque specification from datasheet.
• Overload relay pairing: The 3RT2035 series is commonly paired with the Siemens 3RU2116 / 3RB3026 thermal or solid-state overload relays for motor protection; verify dimensional compatibility and coordination class before specifying the protection scheme.

Alternate Coil Voltages

The 3RT20351Axxx family shares the Size S2 40 A frame with the seed but covers multiple AC coil voltages. Comparison of shared fields:

Notable contrasts among shared keys:

• The seed and 3RT20351AC24 share the same 24 VAC coil but differ in contact current rating (60 A vs. 40 A); verify whether this reflects different utilization categories (AC-3 vs. AC-1) in the ordering code structure.
• 3RT20351AM20 has DPST-NO/NC (1 Form A, 1 Form B) contact form—a mixed pole configuration—while the seed and all other alternates are 3PST-NO. Substitution for power switching roles is not direct.
• Coil power differs: seed lists 210 VA; alternates list 188 VA or 212 VA for the same 24 VAC coil variant—confirm whether this reflects measurement differences or packaging/measurement conditions.
• Encapsulation differs: only the seed and 3RT20351AL20 carry Bulk; all others carry Box. For automated assembly, confirm whether tray vs. bulk orientation is acceptable.

Selection Guidance

The seed represents a 24 VAC coil, Size S2, 40 A frame, 3PST-NO with one NO auxiliary contact, Bulk configuration. Verify the following before committing to a Bill of Materials:

1. Confirm the switching voltage and AC-3 breaking capacity from the Siemens 3RT2 datasheet; these fields drive coordination studies with upstream protection.
2. Confirm the release voltage and holding power for control-circuit design.
3. Confirm whether the 60 A contact rating applies to AC-1 (non-inductive) or AC-3 (motor) duty; if AC-3 applies, the motor FLA must not exceed the 40 A frame rating of the series.
4. If replacing an existing installation, cross-reference the full ordering code (not just the base number) to ensure coil voltage, auxiliary contact arrangement, and packaging all match.

FAQ

Is the 3RT20351AC20 suitable for direct motor starting? The 3RT2035 series is designed for AC-3 motor switching duty. Verify the breaking capacity under the prospective short-circuit current of the installation and confirm coordination with the upstream protective device and any paired overload relay.

What is the difference between the seed (3RT20351AC20) and 3RT20351AC24? Both carry the same 24 VAC coil voltage and the same 3PST-NO contact form. The seed lists a 60 A contact rating and Bulk packaging; 3RT20351AC24 lists a 40 A contact rating and Box packaging. Confirm the utilization category and thermal rating difference from the datasheet before substitution.

Can a 110 VAC coil variant such as 3RT20351AG20 be used in place of the 24 VAC seed? Only if the control-system voltage is 110 VAC. Coil voltage is a fixed selection parameter; the contact arrangement and mounting remain compatible, but the must-operate voltage (93.5 VAC for 3RT20351AG20 vs. 20.4 VAC for the seed) confirms they are not interchangeable without a control-system redesign.